DIY Fuzz Pedal

[soDakKid]

I've built a fuzz pedal but am having some problems, hoping someone here can help out.

What works:
- bypass is clean
- LED goes on/off as expected
- it does make fuzz

What does not work:
- very high noise (60Hz hum) when using a wall-wart. I've tried 3 different ones - I do not have this problem with other pedals. For now I'm using a 9v battery which is quiet.

  - there is a high pitch squeal that the pedal will generate with the right settings - this can be without the instrument even being plugged into it. setting the trimpot to around 4v per the instructions and turning the volume and fuzz past 9 o'clock will generate the squeal - almost like a feed back. I've tried various different trimpot settings between 3 and 6v but it doesn't have any impact.

  - there are also random pops & clicks that the pedal makes when active. this happens whether the instrument is plugged in or not and with different trimpot settings.

  - despite the the issues above it will make nice fuzz as long as the parameters are kept low enough, but once the volume is turned up on the pedal it really falls apart.

What i have done:
  - retouched all solder points

  - validated all wiring

  - i've replaced the original BC108 transistors with BC549CTA equivalents. I did this in hopes of curing the issues above. I validated the pin-outs. This gave a minor improvement, but that's all.

- measurements of Q1 & Q2:
  - Q1:
    b = .58
    c = 1.2
    e = 0

  - Q2:
    b = 1.2
    c = 4.2
    e = .6

  - i've replaced the trip pot with another of the same value after getting some strange readings from using the VM, but ultimately this had no change either.

http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/fuzz_schem.png.html


Thanks in advance.
Brett

[duck_arse]

welcome to the forum, soDakKid.

we always like to look at builds, so can you please post some photos of what you have built, and the layout diagram you were building to? I think your voltages look alright, so it is most likely down to connection problems.

[soDakKid]

thanks duck_arse - here's some photos - let me know if you need anything more specific. FYI - I don't have a direct trimpot replacement as far as physical size goes, but rather am using a 25k pot (same value) in it's place till I order a new one from Digikey.

photos:
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/IMG_3825.JPG.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/IMG_3826.JPG.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/IMG_3827.JPG.html
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/IMG_3828.JPG.html

schematic:
http://www.aronnelson.com/gallery/main.php/v/Schematics-etc/fuzz_schem.png.html

thanks

[Cozybuilder]

To my tired old eyes the solder joints on the switch look iffy

As far as the trim pot, once you have this running right, and the pot is adjusted to give a sound you like, you can measure the resistance actually used and sub a fixed value R for the trimmer.

[thermionix]

To my tired old eyes the solder joints on the switch look iffy

I tend to agree, but I can't really tell if those are shadows or gaps.

Have you tried this in an enclosure yet?  Does moving the wires around have any effect on the squeal?

Your circuit is a copy of a Si Fuzz Face, you probably know.  Like the originals it doesn't have any filtering on the 9v supply.  That's no problem when a battery is used, but most modern pedals that accept wall warts will have this filtering (cap) to help smooth out ripple (hum) from wall warts, as many of them don't do such a good job of that internally.

You could add a cap for this power supply filtering, a good place to solder it in might be at the wall wart jack lugs, since there's not a spot for it on the PCB.  What I don't know is if that would change the sound of the fuzz any, because I've never tried it, and Fuzz Faces are so damn sensitive about everydamnthing.

Personally, I would just use a battery, assuming there's room for one in the enclosure.  A fuzz face is a very low current device, and a battery lasts a long time.  Without the LED (or with the pedal in bypass) a typical 9v battery can last for weeks straight.

[smallbearelec]

The squeal is most likely oscillation resulting from using high-gain transistors in a circuit that's optimized around lower ones. The 150 pf. snubbing cap usually suppresses this. Suggestions: Try a lower gain device in the Q1 position...I like a 2N4123

http://diy.smallbearelec.com/HowTos/BreadboardSiFF/BreadboardSiFF.htm

and/or increase the value of the snubbing cap.

[PRR]

The DC voltages look spot-on?

Which means some of the solder joints do work good. (For now?)

The buzz is because your wall-wart makes crap DC, and your other pedals have DC filters which cut it way down. Add 200 Ohms and 200uFd.

The screech is partly from NOT having something plugged in the front (to hold-down the sensitive input) and mostly from output wires running close to input wires. Metal box will help after you get your layout so the sewer isn't leaking to the well.

[soDakKid]

Hey thanks a lot folks - this is great stuff

@smallbearelec - thanks for the link. I'll order up a few new transistors from Digikey.

Regarding the switch, I tried to be conservative with the solder so as to not get any bridges underneath between the switch & board, but I will retouch and verify with a VM that the connections are good.